Wood bleaching



Finesse Patented Feb 20, 1940 UNITED STATES PATENT OFFICE WQOD BLEACHING Hans 0. Kauffmann, Eggertsville, N. Y., assignor to Buffalo Electro-Ohemical Company, Inc., Buffalo, N. Y.

No Drawing. Application April 13, 1938, Serial No. 201,777

4 Claims. (Cl. 8-111) The present invention relates to bleaching wood and woody materials and more particularly to a method of bleaching and lightening the color of wood and woody materials by subjecting such lution generating active oxygen that is relatively stable at the temperatures at which it is employed. A still further object of the invention is the provision of a bleaching method for woody material. This treatment is facilitated by heating to temperatures of from about 50 to 80 C. or higher and maintained in this temperature range during the bleaching. Impregnation of the of aqueous ammonia, 6 g. of anhydrous sodium pyrophosphate and a wetting out agent capable of reducing the surface tension of the solution.

A remarkable feature of the present invention.-

materials at elevated temperatures to the action wood is eifected while the wood is immersed in 5 of a bleaching bath containing or generating hythe solution since at temperatures above about drogen peroxide. 50 C. any included or dissolved gaseous material It has been recommended heretofore that wood is driven out of the Wood and the bleaching soluand woody materials be bleached by the use of tion permitted to diffuse slowly in the pores of 10 oxidizing agents such as hydrogen peroxide. The the Wood and impregnation obtained to a con- 10 wood or woody material to be bleached was imsiderable depth in large pieces such as mop hanmersed in the hydrogen peroxide containing an dles and the like, while veneer strips are bleached alkali such as sodium silicate but such procedure throughout. has proven expensive and uneconomical due to Depending upon the type of wood, its thickness,

the excessive losses of active oxygen. It has also structure, density and the condition of its sap 15 been proposed to lighten the color of wood and content, that is to say, whether sap laden or seawoody materials by treating such materials with soned, the material is immersed in the heated hydrogen peroxide and potassium permanganate, bleaching solution and the treatment continued Reducing agents such as soluble hydrosulfites for from about one to about ten hours. In genhave been suggested for bleaching woods as has eral, the desired results are obtained in about six 20 oxalic acid. hours.

In these prior methods of wood treatment the Although for purposes of illustration it has been wood or Woody material was often stained a'nddisindicated that hydrogen peroxide is employed as colored due to the precipitation of various chemthe bleaching agent, it will be apparent that icals in or upon the pores of the woody fiber, an materials producing hydrogen peroxide in aque- 25 unsightly and unwanted unevenness being thus ous solution can also be employed, as, for instance, produced that followed the grain of the wood certain per salts such as the perborates, percarmore or less and thus in many instances defeated bonates, and the like, as well as the metallic the very purpose of the treatment, that is, the peroxides, as, for instance, sodium peroxide and production of an even color throughout, miniother soluble peroxides of similar type. This 30 mizing the excessive contrast in Woody materials class of materials is designated herein as soluble often caused by deposition of foreign matter in peroxides. It will, of course, be understood that the grain. hydrogen peroxide is the preferred bleaching An object of the present invention is the proagent since by its employment no residue is left vision of a bleaching method for wood and woody on the bleached material nor is a strong alkali 35 materials that produces a product having an even produced in solution by its employment. color throughout and without a deposit of for- Illustrative of the composition suitable for eign matter due to grain structure of the wood. bleaching wood may be mentionedthe following A further object of the invention is to provide in which one liter of solution contains 160 cc.

'40 a hydrogen peroxide bleaching solution, or sohydrogen peroxide of 100 volume strength, 15 cc.

wood or woody fibers that will bleach to a con-- is that these alkaline hydrogen peroxide solu- 45 siderable depth and will bleach ply wood and tions containing a pyrophosphate such as the veneer strips throughout the body of the strip tetrasodium pyrophosphate or disodium pyroas well as the superficial surface thereof. phosphate are extraordinarily stable in the pres- In accordance with the procedures of the presence of Wood within the range of temperature. ent invention the wood and Woody material is employed for bleaching the wood. It is a rec- 50 saturated and impregnated with the bleaching agent while immersed in the bleaching solution which is maintained at elevated temperatures. In order to obtain evenness of bleach the solution is circulated over and about the wood and ognized fact in bleaching of textiles that soluble pyrophosphates stabilize hydrogen peroxide solutions only on the acid side or if the solution have a pH higher than about 7, then only at temperatures lower than about 45 C.

The following table sets forth the active oxygen content of baths of the composition outlined above at various times indicated. In one bath 58.7 g. of a burl myrtle veneer were immersed at to C. with approximately an 8 to 1 liquor ratio, while in another 56.0 g. of boiled cotton goods wereimmersed in a solution of the same composition, the temperature of which was 60 to 65 C. and a liquor ratio of approximately 8 to 1. The volume of solution used in each case was 450 cc. The active oxygen content is expressed in terms of one-half normal potassium permanganate.

Table I Cubic centimeters of n04 Time in minutes Wood Cotton The strength of the original solutionin terms of active oxygen expressed in cc. of

was 11.2. It will be noted that the active oxygen content of the bath when used on cotton goods decreases very rapidly, while there is only a slight decrease in active oxygen content in the bath in contact with wood.

In comparing the stabilizing action of sodium pyrophosphate with that of sodium silicate a sample of 58.8 g. of burl myrtle veneer and 58.0 g. boiled cotton goods were separately immersed in 450 cc. of the following solution and treated for the time indicated in the table below at a temperature of 60 to 65 C. The oxygen content of the original solution expressed in terms of cc. of

was 11.2. The composition of the solution was as follows: cc. of the aqueous solution contain cc. of hydrogen peroxide, 100 volume, 15 cc. aqueous ammonia, 23 cc. silicate (42 B.) and the same quantity of the wetting out agent as specified above.

An examination of the above tables will point out strikingly the advantages of pyrophosphate used in connection with hydrogen peroxide solution in wood bleaching. When it is recalled that pyrophosphate is recognized as being unsuitable for addition to alkaline peroxide baths for use at elevated temperatures, the remarkable advantage of pyrophosphate addition to alkaline peroxide solutions for bleaching wood is strikingly shown. Thus, Table 11 indicates that wood degrades peroxide solutions stabilized with silicate more rapidly than does cotton, and similar action might be expected irrespective of the stabilizer used in the solution due to the presence in wood of substantially larger quantities of catalytic materials decomposing hydrogen peroxide than are present in the purer material, cotton. However, Table I shows a remarkable superiority of pyrophosphate as a stabilizer for peroxide solutions for wood over silicate and shows further that the pyrophosphate enervates or destroys the excess catalytic action of wood over cotton.

1 claim:

1. The process of bleaching wood which comprises treating the wood with a solution of a peroxide containing a pyrophosphate.

2. The process of bleaching wood which comprises immersing the wood in a solution of a peroxide containing a pyrophosphate.

3. The process of bleaching wood which comprises immersing the wood in a solution of a peroxide containing a pyrophosphate and heating the solution to a temperature of between about 45-85 C.

4. The process of bleaching wood which comprises treating the wood with a solution of a soluble peroxide and containing at least 0.6% of a pyrophosphate.

HANS O. KAUFIEMANN. 

